In the past, as a system for detecting whether or not a person is inside (is present or is not present in) a building or a specific room therein (a presence detection), a system has been proposed that detects the presence/absence of a person by directly irradiating a person with microwaves having a high linearity, such as 10.5 GHz and/or the like, and receiving reflected waves. However, when the attempt is made to use microwaves, specialized transmission equipment and receiving equipment is necessary, so the system as a whole has a high cost. In addition, with this method the presence/absence of a person is detected using the linearity of microwaves, so the detection range is limited to the direction in which the equipment emits the microwaves. Consequently, this system is not suitable to applications such as presence detection in a room as a whole.
In addition, a system has also been proposed that detects the movement of a substance whose temperature differs from the surroundings using an infrared sensor. This system could easily be composed by simply providing an infrared receiver. However, this system uses weak infrared rays generated from humans and thus is not suitable for applications such as presence detection in a room as a whole due to sensitivity issues.
As a system for detecting the presence of a person simply yet in a wide area, a human movement detection system has been proposed that uses as a transmission source radio waves transmitted from a wireless system accomplishing services at a constant transmission power such as TV broadcast waves and/or the like (for example, see Patent Literature 1). This system detects the presence of a person by constantly detecting the range of fluctuations in radio wave reception levels using the principle that the reception level of radio waves fluctuates in accordance with changes in the multipath environment in a room due to a person's movements.
With this person behavior detection system, it is possible to realize a simple presence detection system that does not require special hardware and that uses wireless communication equipment set up in a room for other objectives.
In addition, with this system, presence detection is possible in the entirety of an expansive room because reflected waves that propagate throughout the room as a whole are used, not only radio waves transmitted directly to the receiver from the transmitter.